Movable contact structure for a molded-case electric circuit breaker



Aug. 25, 1970 J. H. LEONARD 3,525,837 MOVABLE CONTACT STRUCTURE FOR A MOLDED-CASE ELECTRIC CIRCUIT BREAKER Filed Nov. 18, 1968 5 Sheets-Sheet 1 N JAMES H.'LEONARD y 7W E}? 1970 J. H. LEONARD 3,

MOVABLE CONTACT STRUCTURE FOR A MOLDED-CASE ELECTRIC CIRCUIT BREAKER Filed NOV. 18, 1968 5 Sheets-Sheet 2 Aug; 25, 1970 J. H. LEONARD MOVABLE CONTACT STRUCTURE FOR A MOLDED-CASE ELECTRIC CIRCUIT BREAKER 5 Sheets-Sheet 3 Filed Nov. 18, 1968 I/VVE/VTOR. JA MES H. LEONARD Aug. 25, 1970 J. H. LEONARD 3,525,337

' MOVABLE CONTACT STRUCTURE FOR A MOLDED-CASE ELECTRIC CIRCUIT BREAKER Filed Nov. 18/ 1968 5 SheetsSheet 4 INVENTOR. JAMES H. LEONARD Aug. 25, 1970 v J. H. LEONARD MOVABLE CONTACT STRUCTURE FOR A MOLDED-CASE} ELECTRIC CIRCUIT BREAKER 5 Sheets-Sheet 5 Filed Nov. 1 8, 1968 United States Patent Office 3,525,837 Patented Aug. 25, 1970 MOVABLE CONTACT STRUCTURE FOR A MOLDED-CASE ELECTRIC CIRCUIT BREAKER James H. Leonard, Cedar Rapids, Iowa, assiguor to Square D Company, Park Ridge, 11]., a corporation of Michigan Filed Nov. 18, 1968, Ser. No. 776,608 Int. Cl. H01h 1/22, 1/34 US. Cl. 200-166 22 Claims ABSTRACT OF THE DISCLOSURE tact carrier.

This invention relates to a movable contact structure of an electric switch, and more particularly to an improved movable contact structure having main and arcing contact arms and particularly suitable for use in a molded-case circuit breaker.

In order to increase the interrupting ability and current-carrying capacity of molded-case circuit breakers without material increase in their size, it is necessary to improve the movable contact structures. While certain prior art circuit breakers, such as the one disclosed in US. Pat. No. 3,355,685, issued Nov. 28, 1967, have relatively large current-carrying capacity and interrupting ability for their size, usage requirements demand that these ratings be increased without exceeding certain size limitations. The movable contact structure of this invention meets this demand.

Accordingly, an object of this invention is to provide an improved movable contact structure for a moldedcase circuit breaker which permits the circuit breaker to have increased current-carrying and current-interrupting ability.

Another object is to provide an improved movable contact structure capable of exerting relatively large contact pressures.

Another object is to provide an improved movable contact structure having a movable main contact arm, a movable arcing contact arm, a carrier for the contact arms, and contact pressure spring means between the contact arms and the carrier.

Another object is to provide an improved movable contact structure having main and arcing contact arms and a combination contact arm carrier and contact pressure spring means.

A further object is to provide an improved movable contact structure having a main contact arm pivoted in a recess defined by a pair of complementary hook-shaped extensions of a terminal plate.

Additional objects and advantages will become apparent from the following description wherein reference is made to the drawings, in which:

FIG. 1 is a top view, with an operating handle and a pair of terminal covers and most of a main cover removed, of a three-pole molded-case circuit breaker having movable contact structures in accordance with this invention;

FIG. 2 is a sectional view, with the covers in place, of the circuit breaker of FIG. 1 showing the movable contact structure of the center pole and taken generally along the line 22 of FIG. 1;

FIG. 3 is an exploded perspective view of the center one of the movable contact structures of the circuit break er shown in FIG. 1;

FIG. 4 is a perspective view of a contact arm carrier of the movable contact structures of the outer poles of the circuit breaker of FIG. 1;

FIG. 5 is a side view showing an alternative embodiment of a movable contact structure in accordance with this invention;

FIG. 6 is a top view of the movable contact structure of FIG. 5 with certain parts removed for clarity;

FIG. 7 is an exploded perspective view of the movable contact structure of FIGS. 5 and 6;

FIG. 8 is a perspective view of an alternative embodiment of a leaf spring for the movable contact structure of FIGS. 5, 6 and 7; and

FIG. 9 is a fragmentary side view showing an alternative embodiment of a main pivot axis for the movable contact structure of FIGS. 5, 6 and 7.

A three-pole molded-case circuit breaker 20 having movable contact structures in accordance with the invention is shown in FIGS. 1 and 2. The circuit breaker 20, with the exception of the movable contact structures, is similar to the circuit breaker disclosed in the abovementioned US. patent to which reference may be made for more detailed description, and includes a moldedcase comprising a base 22, a main cover 24, and a pair of oppositely disposed terminal covers 25 each removably secured to the cover 24 by means of one or more screws 26.

The case of the circuit breaker 20 is divided into three internal compartments or pole spaces 28, 29,and 30, one for each of the three poles of the circuit breaker. To this end, the base 22 is provided with a pair of opposed parallel side walls 22a and 22b and a pair of spaced intermediate walls 220 and 22d parallel to the side walls 22a and 22b, and the cover 24 is provided with corresponding depending side and intermediate walls (not shown). The opposite end portions of the depending side walls and intermediate walls of the cover 24 are recessed for reception of the terminal covers 25.

Two pairs of alignment pins 27 are provided for the base 22 and cover 24, the pairs of pins 27 being respectively adjacent the opposite ends of the intermediate walls 22c and 22d as shown in FIG. 1. After alignment of the base 22 and cover 24 by the pins 27, the base 22 and cover 24 are riveted together in a well-known manner.

As viewed in FIGS. 1 and 2, the right-hand ends of the compartments 28, 29, and 30 within the base 22 are provided with transverse walls 22e, 22 and 22g, respectively. The left-hand ends of compartments 28, 29, and 30 are provided with like transverse walls, only the one for the end of the center compartment 30 being shown at 22h in FIG. 2.

Adjacent the right-hand end of the center compartment 30, a terminal strap 34 of a center pole is secured to the base 22 by a plurality of screws 35. The terminal strap 34 has an outer end portion disposed in a connector cavity 33 (FIG. 2) and extends inwardly into the center compartment 30 through an opening in the transverse wall 22g. An inner end portion of the terminal strap 34 within the compartment 30 is provided along its longitudinal axis with a raised main stationary contact portion 36, an arcing contact portion 36a, and an arc runner portion 37. The outer end portion of the terminal strap 34 may be secured to a connector body (not shown) by means of two screws which thread into respective threaded apertures 38. The center compartment 30 also houses an arc chute 39 comprising a plurality of arc-dissipating and deionization,plates 39a held in assembled relationship by two fiberboard members 3%, only one of which is shown in FIG. 2. The are chute 39 is positioned above the arcing contact portion 36a and are runner portion 37v to dissipate arcs produced upon interrupting the current flowing through the circuit breaker 20.

Adjacent the left-hand end portion of the circuit breaker as viewed in FIGS. 1 and 2, the center compartment is provided with a relatively thin terminal strap 40 of the center pole secured to the base 22 by means of a screw 42. The terminal strap 40 extends inwardly into the center compartment 30 through an opening in the transverse wall 22h, an outer end portion being securable to a connector body (not shown) by means of two screws threadable respectively into aligned threaded apertures 44 in the terminal strap 40 and in a relatively short metal plate 45 secured by the screw 42 to the outer end portion of the terminal strap 40 to provide additional thread engagement for the two connector-securing screws. The terminal strap 40 is thinner than the terminal strap 34 so that its resistance is greater causing more heat to be generated therein by the flow of current, as explained in the above-mentioned patent.

As shown in FIG. 1, each of the two outer poles in the outer compartments 28 and 29 is identical with the center pole as so far described.

The circuit breaker 20 includes a trough extending transversely of the circuit breaker 20 into each of the compartments 28, 29, and 30 and which is of sufiicient size to house a suitable tripping means for the circuit breaker 20 extending the length of the trough, the tripping means preferably being like that disclosed in the above-mentioned patent. The case of the circuit breaker 20 includes, as an integral part of the cover 24, a cover portion 51 having an aperture 53 which provides access to a single adjusting means (not shown) and associated pole pieces of the tripping means within the trough 50. A slidable control member 52 controlling the single adjustment means is exposed through the aperture 53 in the cover portion 51. The control member 52 is provided with a slot 52b accessible for the reception of a screwdriver by which the control member 52 may be shifted, the slot 52b also serving as a position indicating means.

A suitable operating mechanism 55 of the circuit breaker 20 is within the compartment 30 and includes numerous interconnecting movable parts, as indicated by dashed lines of FIG. 2, the movable parts being shown in the OFF .position of the circuit breaker 20. The operating mechanism assembly 55, which is preferably like that disclosed in the above-mentioned patent, has a metal top plate 56 (FIG. 1) to which an operating handle 58 (FIG. 2) is secured. The handle 58, formed of insulating material, extends through an aperture 24a of the cover 24 for external operation of the operating mechanism 55. The handle 58 has side portions 59, only one of which is shown in FIG. 2, which fit adjacent to the opposite transverse sides of the top plate 56.

The operating mechanism 55 controls the operation of a movable contact structure 60a of the center pole and movable contact structures 60b of the respective outer poles which are in accordance with this invention. The movable contact structure 60a of the center pole is disposed beneath the operating mechanism 55 in the compartment 30, and is electrically connected by means of screws 61 to the inner end portion of the terminal strap 40 as will be further described. The mechanism 55 has a drive pin as shown in the above-mentioned patent connected to the movable contact structure 60a, as later described, to impart the movement of the mechanism 55 thereto and thus operate the movable contact structure 60a to its OFF, ON, and TRIPPED positions.

The movable contact structure 60a of the center pole includes a contact arm carrier 62a which serves as a driving means for contact arms, as later described, and which is pivotally mounted adjacent one of its ends, the lefthand end as viewed in FIG. 2, on a pair of stub-axles 63 carried by spaced upstanding cars 63g of a bracket 63b secured to the base 22 by screws 63d, the axles 63 being received in respective openings 620 in respective side portions 62d of the carrier 6211 (FIG. 3). The side portions 62d also have respective openings 62c through which the drive pin passes.

Adjacent its free end, the carrier 62a carries a generally rectangular crossbar 64 formed of insulating materi l. The carrier 62a is provided with two aligned rows of apertures 65, each row extending transversely of the carrier near the free end thereof, the apertures providing a means for attaching a generally U-shaped bracket 66a to the carrier 62a. The U-shaped bracket 66a fits over the crossbar 64 and has spaced protruding portions (not shown) on the free ends of its leg portions which extend through the respective apertures 65, the protruding portions securing the bracket 66a and thus the crossbar 64 to the carrier 62a by capturing the protruding portions within the apertures in some conventional manner such as by bending the portions over after their insertion through the apertures.

The crossbar 64 carries two relatively thin barriers 67 made of insulating material, the barriers 67 being positioned respectively adjacent to the intermediate walls 22c and 22d in the compartments 28 and 29, respectively.

Each of the movable contact structures 60b of the two outer poles in the outer compartments 28 and 29 is provided with a contact arm carrier 62b similar to the carrier 62a of the center pole except for the shape of the side portions thereof. Each of the two outer carriers 62b has side portions 62 shaped as shown in FIG. 4, and is provided with a U-shaped bracket 66b, similar to the U- shaped bracket 66a, which secures respective end portions of the crossbar 64 thereto. Thus, while the carrier 62a is pivoted on the pair of stub-axles 63 and driven by the drive pin (not shown), the carriers 62b of the two outer poles are driven by the crossbar 64. The carriers 62b may be mounted on a pair of stub-axles 63 in the same manner as the carrier 62a, or may be arranged so that respective depending ears of the side portions 62 merely rock against raised portions of the bottom wall of the base 22.

Each of the movable contact structures 60a and 60b comprises a movable contact arm assembly 70 suspendable from either of the carriers 62a or 62b and shown best in FIG. 3, having a center arcing contact arm 71, provided with an arcing contact 71a, and two outer main contact arms 73, provided with respective movable contacts 73a. Because the movable contact arm assemblies 70 for the movable contact structures 60a and 60b are identical, only one will be described.

The arcing contact arm 71 and the two main contact arms 73 are connected, respectively, at one of their respective end portions, to tines of a flexible connector 74 by any suitable means such as by rivets 77, the arcing contact arm having its free end portion extending beyond the free end portions of the two main contact arms 73. The flexible connector 74 is formed of a plurality of relatively thin layers of flexible metal and has a base portion 74a having apertures 75, a center tine 74b, and two shorter outer tines 740, the tines extending from the base portion 74a. The center tine 74b is connected to the arcing contact arm 71 by one of the rivets 77. The two shorter outer tines 740 are connected respectively to the two outer main contact arms 73 each by one of the rivets 77. The flexible connector 74 is secured at its base portion 74a to a connector terminal plate 76 in any suitable manner such as by rivets 77a received in the respective apertures in the base portion 74a. The connector terminal plate 76 is connected to the terminal strap 40 by means of the screws 61 as previously described. Thus, the tine 74b serves to define an arcing pivot axis for the arcing contact arm 71, and the tines 74c serve to define main pivot axis for the respective contact arms 73.

End portions of a pair of leaf springs 78 are connected respectively to the free end portions of the two outer tines 740 by the same rivets 77, respectively, that secure the contact arms 73 to the tines 74c. Each of the leaf springs 78 comprises two juxtaposed metal fingers 78a and 78b extending outwardly from the free end portion of its associated one of the tines 74c, the finger 78b of each underlying the overlapping finger 78a and extending beyond the finger 78a. The outer end portions of the fingers 78b respectively engage the upper surfaces of the main contact arms 73. Each leaf spring 78 projects outwardly from the free end portion of its associated tine 74c in an arc-like manner, concave downwardly, to provide a downward bias to the movable main contact arm 73 toward the complementary main stationary contact portion 36.

A downward force on the leaf springs 78 is provided by means of a bracket 80 connected to the center tine 74b by the rivet 77 that secures the arcing contact arm 71 to the tine 74b. The bracket 80 is generally U-shaped with its bight portion 80a attached to the center tine 74b. The leg portions of the bracket 80 project upwardly and perpendicularly from the bight portion, and the end portions of the leg portions are provided with out-turned flange portions 80b and 800 which are substantially parallel to the bight portion 80a and which respectively overlap the outer end portion of the respective fingers 78a of the leaf springs 78 and abut thereagainst.

Immediately adjacent to the point of attachment of the arcing contact arm 71 to the center tine 74b, there is a non-threaded recess 83 in the arcing contact arm 71 in which one end portion of a stud 84 is received. Each of the carriers 62a and 62b has an opening, positioned rearwardly of the free ends of the carriers with respect to the apertures 65, in which the stud 84 is threaded. The studs 84 provide adjustable stop means for altering the position of the arcing contact arm 71 with respect to the associated carriers 62a and 62b and the main contact arms 73, thereby to ensure the desired angular position of the arcing contact 71a with respect to the stationary arcing contact portion 36a. Toward the free end portions from the apertures 65 in each of the carriers 62a and 62b are three transversely aligned and spaced-apart apertures 85 which accommodate respective screws 86. Threaded end portions of the screws 86 are received in respective threaded apertures 87 in the associated arcing contact arms 71 and the main contact arms 73 and extend upwardly through the respective apertures 85 in the carriers 62a and 62b to provide supporting means for the contact arms 71 and 73, thus fixing the arms 71 and 73 at a predetermined position relative to each other prior to closing the contact structures 60a and 60b, and to provide an overtravel adjustment for the respective carriers 62a and 62b.

Each of the carriers 62a and 62b is provided with an aperture 88 in its extreme free end portion which accommodates a helical contact pressure spring 89 (FIG. 2) having a screw-type tension adjustment means 90 (FIGS. 1 and 2) each spring 89 resting in a spring seat 91 in the free end portion of its associated arcing contact arm 71. The springs 89 provide lost motion means for overtravel of the carriers 62a and 62b with respect to the associated arcing contact arms.

In the operation of the circuit breaker 20 to the ON position, clockwise movement of the handle 58 as viewed in FIG. 2 imparts movement to the movable contact structure 60a by means of the drive pin (not shown) of the operating mechanism 55, which drive pin connects with the side portions 62d of the carrier 62a as described heretofore. The carrier 62a is thereby driven clockwise as viewed in FIG. 2 about its pair of stub-axles 63 to effect a corresponding movement of the associated movable contact arm assembly 70. As the free end of the carrier 62a is driven downwardly, the crossbar 64 acts as a driving means and causes the free end portions of each of the carriers 62b by the two outer poles to be driven downwardly simultaneously, thus effecting concurrent downward movement of all three movable contact arm assemblies 70. The arcing contact arm 71 of each contact arm assembly 70 is adjusted by means of its adjustment means 90, its associated one of the studs 84, and its associated one of the screws 86 so that the movable arcing contact 71a makes initial contact with its associated stationary arcing contact portion 36a before the two main movable contacts 73a make contact with their associated main stationary contact portion 36 and separates from the contact portion 36a after the main contacts 73a separate from the contact portions 36.

The synchronized operation of each of the arcing contact arms 71 with their associated movable main contact arms 73, and the synchronized operation of the two movable main contact arms 73 with each other, is provided by adjustmment of their respective screws 86.

An alternative embodiment of a movable contact arm assembly in accordance with this invention is shown at in FIGS. 5, 6, and 7, and, like the contact arm assembly 70, may be used either with the contact arm carrier 62a or 62b of the movable contact structures 60a or 6012, respectively. FIG. 5 shows the contact arm assembly 100 being used with the carrier 62b to form an outer pole contact structure.

The movable contact arm assembly 100 includes a plate-like arcing contact arm 101 provided with a movable arcing contact 101a which may be of a suitable refractory material, and an optional arcing tip 101b on its free end portion. A plate-like main contact arm 102 is provided with a movable main contact 102a on its free end portion which may be of a non-refractory material. A relatively shallow transverse groove or recess 102b is formed in th upper surface of the main contact arm 102 generally centrally thereof. The arcing contact arm 101 is both shorter and narrower than the main contact arm 102 and pivots about a ridge-like projection 103 extending the entire width of the arcing contact arm 101 on the end opposite its free end and resting within the recess 102b to provide an arcing pivot axis for the arcing contact arm 101.

The assembly 100 further includes a connector terminal plate 105 and a flexible connector 106. The flexible connector 106 is formed of a plurality of interwoven strands of flexible metal and electrically and mechanically connects the main contact arm 102 to the terminal plate 105 to provide an additional path of current conduction and a restraint upon the physical separation thereof, respectively. If desired, a similar flexible connector (not shown) may be provided to electrically and mechanically connect the arcing contact arm 101 to the main contact arm 102. Although, as shown, the flexible connector 106 has three relatively narrow strips of flexible metal, it may comprise but one wider strip if desired.

The terminal plate 105 is connected to the base 22 by a pair of screws 104 and to the terminal strap 40 by means of a pair of screws 104a in a manner similar to the connection of terminal plate 76 to the terminal strap 40, and has a hook-shaped extension 107 which receives a ridge-like projection 108 extending the entire width of the main contact arm 102 on the end opposite to its free end and providing a main pivot axis for the pivotal movement of the contact arm assembly 100.

The arcing contact arm 101 is resiliently held in position with respect to the main contact arm 102 by a U- shaped leaf spring 109 having an upper and a lower leg portion. As shown in FIGS. 5 and 6, the leaf spring 109 is oriented in fiatwise relation to the contact arm carrier 62b and the contact arms 101 and 102, with the free end portion of the lower leg portion engaging the upper surface of the arcing contact arm 101 generally centrally thereof, at a position in alignment with the line of operat ing force provided to open and close the contact-s of the circuit breaker and which is exerted through the medium of the crossbar 64, in the manner heretofore described in connection with the contact arm assembly 70. The relative position of the free end portion of the lower leg portion of the spring 109 on the arcing contact arm 101 and with respect to the main pivot axis of the assembly 100 determine the proportions of the driving or operating force that Will be applied to the arcing contact arm 101 and main contact arm 102.

The upper leg portion of the leaf spring 109 is provided near its free end portion with two aligned rows of apertures 110 extending transversely of the longitudinal axis of the leaf spring 109. The apertures 110 underlie and align respectively with the correspondingly located apertures 65 in either of the carriers 62a and 62b. The apertures 110 provide a means for securing the upper leg portion of the leaf spring 109 to the respective carriers 62a and 62b by the reception of the protruding portions of the brackets 66a and 66b, respectively, in the manner heretofore described in connection with the embodiment of FIGS. 1 through 4. The stud 84 and tension adjustment means 90 are not provided in the contact arm assembly 100 as the positioning of the leaf spring 109 and the geometry of the assembly 100 make these adjustments unnecessary.

The free end portion of the upper leg portion of the leaf spring 109 does not extend beneath the apertures 85 of the carriers 62a and 62b. A pair of the screws 86, extending through the outer two apertures 85, provide synchronized adjustment of the movable contact arm assembly 100, and extend from the carriers 62a and 62b,

respectively, so that each of the pairs of screws 86 is received within a pair of threaded apertures 111 (FIG. 6) provided in the opposite corners of the free end portion of each of the associated main contact arms 102.

As shown in FIG. 8, an alternative embodiment 109a of the leaf spring 109 may be provided so that the free end portion of the upper leg portion of the leaf spring 109 is extended to include a row of spaced-apart apertures 112 corresponding to the apertures 85. The apertures 110 provide a means for securing the leaf spring 109a directly to the crossbar 64 and the apertures 112 may contain the associated pair of screws 86 to thus eliminate the need for the two outer pole carriers 62b. Thus the leaf spring 109a serves both as a contact carrier means and as a contact pressure spring.

An alternative embodiment providing a different structure for a pivot axis pivoting a main contact arm is shown in FIG. 9. Referring to FIG. 9, connecting end portions of a main contact arm 113 similar to the contact arm 102 and a pair of terminal plates 114 and 115 are shaped to provide a modified knuckle joint about which the arm 113 pivots between contact open and closed positions. The terminal plate 114 is similar to the terminal plate 105, and the terminal plates 114 and 115 are positioned in flatwise-stacked relationship and are connected together by a pair of screws 116 intermediately of their length, only one screw 116 being shown in FIG. 9. The terminal plates 114 and 115 have oppositely facing hook-shaped extensions 114a and 115a, respectively, on like end portions thereof, which extensions 114a and 115a engage opposite surfaces of an elongated generally cylindrical prominence 113a on the pivot end portion of the main contact arm 113.

A pair of bosses 117, only one of which is shown in FIG. 9, are positioned on an upper surface of the terminal plate 114 in parallel-spaced relationship to the screws 116 on an opposite side thereof from the extensions 114a and 115a, which bosses serve to space an adjacent lower surface of the terminal plate 115 from the terminal plate 114. The terminal plate 115 provides a parallel current path so that the biasing forces between the plates 114 and 115 increases under high-current fault conditions.

What is claimed is:

1. A movable contact structure for a circuit breaker, said contact structure comprising a main contact arm having contact means at one of its end portions, an arcing contact arm having contact means at one of its end portions, a terminal plate, connecting means connecting the other end portion of the main contact arm both electrically and mechanically to the terminal plate and providing for pivotal movement of the main contact arm about a first pivot axis at said other end portion thereof, pivot means for the arcing contact arm defining a second pivot axis parallel to said first pivot axis and providing an electrical connection between the arcing contact arm and the terminal plate, said second pivot axis being positioned between the end portions of the main contact arm, a contact carrier means positioned in flatwise relationship to the main and arcing contact arms, spring means biasing the main and arcing contact arms in one direction about their respective pivot axes, and adjusting means at the free end portion of the carrier means connecting said one end portion of the main contact arm to the carrier means for adjustably positioning said one end portion of the main contact arm at a predetermined distance from said carrier means thereby to adjust the biasing force of the spring means.

2. A movable contact structure as claimed in claim 1 wherein said spring means comprises a U-shaped strip of spring metal having a pair of leg portions, one of said pair of leg portions comprises said carrier means and the other of said pair of leg portions has its free end bearing against the arcing contact arm between the second pivot axis and said one end portion of the arcing contact arm.

3. A movable contact structure as claimed in claim 1 wherein said first pivot axis is defined by a hook-shaped extension of the terminal plate which pivotally receives said other end portion of the main contact arm.

4. A movable contact structure as claimed in claim 3 wherein said hook-shaped extension is a first hook-shaped extension, said terminal plate has a second hook-shaped extension facing the first hook-shaped extension to define a substantially cylindrical opening therebetween, said other end portion of the main contact arm is pivotally received within said opening.

5. A movable contact structure as claimed in claim 4 wherein said terminal plate comprises two electrically interconnected plate members in flatwise-stacked relationship to each other, and said first and second hookshaped extensions are on said plate members, respectively.

6. A movable contact structure as claimed in claim 1 wherein the carrier means is pivoted at one of its end portions about a third axis adjacent said first pivot axis and parallel to said first and second pivot axes.

7. A movable contact structure as claimed in claim 6 wherein said one end of the arcing contact arm extends further from the third pivot axis than does said one end of the main contact arm.

8. A movable contact structure as claimed in claim 6 wherein said second pivot axis is on said main contact arm, said spring means is interposed between the carrier means and the arcing contact arm and biases the arcing contact arm and main contact arm away from the carrier means about their respective pivot axes, and said spring means comprises a U-shaped strip of spring metal having a pair of leg portions with a free end of one of said pair of leg portions secured to the carrier means and a free end of the other of said pair of leg portions bearing against the arcing contact arm between the second pivot axis and said one end portion of the arcing contact arm.

9. A movable contact structure in accordance with claim 1 wherein said main contact arm is a first main contact arm, a second main contact arm is provided having contact means at one of its end portions, said connecting means includes means connecting the other end of the second main contact arm both electrically and mechanically to the terminal plate and provides for pivotal movement of the said second main contact arm about a pivot axis at said one end portion thereof and aligned with said first pivot axis, said spring means includes a pair of springs interposed between the carrier and the first and second main contact arms biasing the first and second main contact arms away from the carrier about their respective pivot axes, and said adjusting means includes means for adjustably positioning said one end portion of the first and second main contact arms at predetermined distances from said carrier means thereby to adjust the biasing force of said spring means.

10. A movable contact structure as claimed in claim 9 wherein the connecting means comprises a flexible connector including a plurality of relatively thin flexible metal strips stacked one upon the other, said flexible connector has a base portion secured to the terminal plate and has first and second parallel-spaced tines protruding in the same direction from the base portion, and the other end portions of the first and second main contact arms are connected to the free end portions of the first and second tines, respectively.

11. A movable contact structure as claimed in claim 10 wherein said flexible connector has a third tine protruding in the same direction between and parallel to said first and second tines, and said other end of said arcing contact arm is connected to the free end portion of the third tine.

12. A movable contact structure as claimed in claim '11 wherein said first and second tines define the first pivot axis and the third tine defines the second pivot axis.

13. A movable contact structure as claimed in claim 11 wherein adjustable stop means is interposed between the carrier means and said other end of the arcing contact arm to alter the effective position of the second pivot axis.

14. A movable contact structure as claimed in claim 11 wherein a U-shaped bracket is secured to the third tine and has flange portions extending outwardly from the free end portions of its respective legs, and said springs comprise a pair of bowed leaf springs interposed between the main contact arms, respectively, and the flange portions.

15. A movable contact structure as claimed in claim 14 wherein the bowed leaf springs have like end portions bearing respectively against the first and second main contact arms and central portions bearing respectively against said flange portions.

16. A movable contact structure as claimed in claim 14 wherein said adjusting means includes a helical spring interposed between the arcing contact arm and the carrier means.

17. A movable contact structure for a molded-case circuit breaker, the contact structure comprising a movable contact arm assembly including a main contact arm and an arcing contact arm, a contact arm carrier having mounting means at one end portion thereof pivotally mounting the carrier about a first axis and supporting means at its other end portion supporting the movable contact arm assembly, said main contact arm having one end portion pivoted about a second axis parallel to the first axis and having a movable main contact on its other end portion, the arcing contact arm having one end portion pivoted about a third axis parallel to the first axis and having a movable arcing contact on its other end portion, and a biasing means positioned between the carrier and the contact arms and biasing the contact arms away from the carrier about said second and third axes.

18. A plurality of movable contact structures each as claimed in claim 17 comprising a center contact structure and two outer contact structures, the carriers thereof being generally flat and the carrier for the center contact structure including perpendicularly depending side portions having apertures, respectively, for receiving a drive pin of an operating mechanism for the circuit breaker, a crossbar secured to said other ends of the carriers for driving the two outer contact structures when the drive pin of the operating mechanism drives the carrier for the center contact structure.

19. A plurality of movable contact structures as claimed in claim 18 wherein each of said other end portions of the carriers has a pair of transversely aligned and spaced-apart rows of apertures, U-shaped brackets are fitted over the crossbar above the respective pairs of rows of apertures, and each U-shaped bracket has protruding fastening portions on the free ends of its leg portions received within the pair of rows of apertures of the associated one of the carriers.

20. In a movable contact structure for a circuit breaker, said contact structure comprising a main contact arm having contact means at one of its end portions, an arcing contact arm having a contact means at one of its end portions, a terminal means, connecting means connecting the other end portion of the main contact arm both electrically and mechanically to the terminal means and providing for pivotal movement of the main contact arm about a first pivot axis at said other end portion thereof, pivot means for the arcing contact arm at the other end portion thereof defining a second pivot axis parallel to said first pivot axis and providing an electrical connection between the arcing contact arm and the main contact arm, said second pivot axis being positioned on the main contact arm between the end portions thereof, and movable driving means for rocking the contact arms about their respective pivot axes, the improvement characterized in that an interconnection between the movable driving means and the contact arms comprises a U-shaped spring having a pair of leg portions, one of said leg portions being attached at its free end portion to the movable driving means and the other of said leg portions being positioned against the surface of the arcing contact arm facing away from the main contact arm thereby to transfer the force of the movable driving means to both the arcing contact arm and the main contact arm.

21. A movable contact structure as claimed in claim 20 wherein the movable driving means is a contact carrier plate pivoted about a third pivot axis parallel to said first and second pivot axes.

22. A movable contact structure as claimed in claim 20 wherein the movable means is an insulating crossbar of the circuit breaker.

References Cited UNITED STATES PATENTS 3,198,924 8/ 1965 Brurrrfield et a1 200- 3,218,428 11/1965 Gauthier 200-170 3,268,702 8/1966 Gryctko 200-170 3,355,685 11/ 1967 Leonard 335-8 3,365,561 1/1968 Jencks et al.

HERMAN 0. JONES, Primary Examiner US. Cl. X.R. 

